The present invention relates to focusing screen master and manufacturing method thereof for manufacturing focusing screens to be used in camera or the like.
Focusing screens to be used in camera or the like are generally fabricated as follows. Specifically, a focusing screen master having a microlens array formed thereon is first used as a master block to fabricate a metal mold or a concave metal mold is fabricated by transferring a form further from the master block. These metal molds are then used in fabrication of the focusing screen by resin forming. A focusing screen having such microlens array formed thereon is capable of being controlled in disposing pitch between microlenses and microlens height so as to control a required blur level and brightness and is used as the focusing screen in a camera.
As a generally used manufacturing method of microlenses on a focusing screen master, Japanese Patent Application Laid-Open Hei-6-194502 for example discloses the so-called “thermal distortion method” in which a photosensitive material uniformly formed on a substrate is exposed to a lens pattern, developed, and then thermally distorted. A description will now be given by way of FIGS. 1A to 1E with respect to the manufacturing method of microlenses disclosed in the above mentioned publication. First, as shown in FIG. 1A, a photosensitive material 101 capable of thermal distortion is formed into a film having a uniform thickness on a flat substrate 102. Subsequently, as shown in FIG. 1B, the photosensitive material 101 is exposed to light of a microlens array pattern 104 depicted on a quartz photomask 103 (optical patterning 105). As shown in FIG. 1C, then, after developing it to form a rectangular photosensitive material 101a, the rectangular photosensitive material 101a is heated to a temperature above its thermal distortion temperature. Convex lenses 101b having identical configuration are thereby obtained uniformly all over the substrate surface as shown in FIG. 1D.
Subsequently, the substrate side having a microlens array formed thereon where these convex lenses 101b are arranged in an array is subjected to dry etching to transfer the form thereof onto the substrate 102 as shown in FIG. 1E. In this manner, a focusing screen master 106 having microlenses formed thereon is completed.